1. Field of the Invention
The present invention relates to an anti-vibration mechanism and a disk drive device using the same and, more specifically, to an anti-vibration mechanism suitable for use in a small-sized drive device for driving disks, such as CDs (compact disks), CD-ROMs (CD-read only memories), MO (magneto-optical memories) and DVDs (digital versatile disks), and a disk drive using the same.
2. Description of the Related Art
Generally speaking, external vibrations, impacts, etc. are applied to an optical or a magnetic disk drive device. Such vibrations, etc. applied during reproduction cause reading errors to thereby generate errors in reading data, etc.
Conventionally, such errors in reading data due to external vibrations, etc. have been prevented by a structure as shown in FIGS. 7 through 9. FIG. 7 is an essential-part sectional view illustrating a conventional anti-vibration mechanism; FIG. 8 is a plan view showing a conventional disk drive device; and FIG. 9 is a plan view showing a first chassis of a conventional disk drive device. As shown in FIGS. 7 through 9, this disk drive device is at least equipped with a first chassis 1 supported by an outer case (not shown), and a second chassis 2 which carries a rotation drive motor 25 to which a turntable 24 is mounted, a reproduction head 20 consisting of an optical head or the like, etc.
Formed in the upper wall 1a on the upper side of the first chassis 1 are a substantially rectangular first hole 1b, situated at the center thereof, a substantially rectangular second hole 1c connected to the first hole 1b, and a plurality of circular mounting holes 1g arranged along the longitudinal side edges of the first hole 1b (for example, two on either side, i.e., four in total).
Arranged on the second chassis 2 are a carriage 21 carrying the reproduction head 20, a screw shaft 22 for driving this carriage 21 in the X-direction, a stepping motor 23 for rotating this screw shaft 22 intermittently, and the rotation drive motor 25, to which the turntable 24 is mounted. Further, on opposing longitudinal side edges 2b of the second chassis 2, there are formed a plurality of (for example, two on either side, i.e., four in total) mounting members 2c upwardly bent into an L-shape and having a fork-like forward-end configuration.
The first chassis 1 and the second chassis 2 are arranged so as to be opposed to each other, and the positions at which the plurality of mounting holes 1g of the first chassis 1 are formed respectively correspond to the positions at which the plurality of mounting members 2c of the second chassis 2 are formed, the two chassis 1 and 2 being attached to each other at these positions. The reproduction head 20, the carriage 21, the rotation drive motor 25, etc. are exposed through the first hole 1b of the first chassis 1.
In this disk drive device, the second chassis 2 is suspended from the first chassis 1 by means of an anti-vibration mechanism B using a plurality of (for example, four) vibration proof rubber members, whereby external vibrations, etc. from the first chassis 1 are prevented from being transmitted to the second chassis 2.
FIG. 7 is an essential-part sectional view illustrating a conventional anti-vibration mechanism B. The fork-shaped mounting member 2c of the second chassis 2 is engaged with a peripheral groove 11a of a cylindrical vibration proof rubber member 11. Passed through the circular mounting hole 1g of the first chassis 1 is a screw portion 10b provided on a support portion 10a of a cylindrical bolt 10 passed through a central hole 11b of the vibration proof rubber member 11. The screw portion 10b is threadedly engaged with a hexagon nut 12, whereby the bolt 10 is fastened to the mounting hole 1g, thereby enabling the second chassis 2 to be suspended from the first chassis 1 through the intermediation of the vibration proof rubber member 11.
When the second chassis 2 is thus suspended from the first chassis 1 through the intermediation of the vibration proof rubber members 11 constituting the plurality of anti-vibration mechanisms B, the height dimension between the upper wall (upper surface) of the first chassis 1 and the upper surface of the turntable 24, mounted to the rotation drive motor 25 arranged on the second chassis 2, is definitely determined.
The height dimension between the upper wall (upper surface) of the first chassis 1 and the upper surface of the turntable 24, definitely determined, cannot be adjusted.
Due to their nature, the vibration proof rubber members 11 must be held in a state in which no such stress as torsion or compression is applied thereto since it is difficult to maintain the requisite dimensional accuracy in machining and a predetermined spring constant must be maintained.
The positioning of the first chassis 1 with respect to the second chassis 2 in the X and Y-directions is effected by inserting the cylindrical bolts 10, which extend through the central holes 11b of the plurality of vibration proof rubber members 11, into the circular mounting holes 1g of the first chassis 1 and threadedly engaging the bolts 10 thus inserted with the hexagon nuts 12.
Nowadays, in disk drive devices required to be thinner and disk drive devices equipped with a changer mechanism in which a plurality of disks are stacked together, there are heavier demands for high accuracy in the dimensions of each member constituting the drive device. In the above-described conventional anti-vibration mechanism B, however, the distance between the first chassis 1 and the second chassis 2 is determined by the machining dimension of the vibration proof rubber members (vibration proof members) arranged between the first chassis 1 and the second chassis 2. This leads to a problem in that it is difficult to maintain the requisite dimensional accuracy of the vibration proof rubber members, and, consequently, it is difficult to maintain high accuracy in the distance between the first chassis 1 and the second chassis 2.
Further, the mounting of the vibration proof rubber members to the first chassis is effected by forcing the mounting bolts into the central holes of the vibration proof rubber members and threadedly engaging the bolts with the hexagon nuts, so that, when engaging the hexagon nuts with the bolts, the bolts rotate with the nuts, with the result that torsional stress is applied to the vibration proof rubber members into which the bolts have been forced. This stress applied to the vibration proof rubber members causes variation in the spring constant of the vibration proof rubber members to be generated, with the result that a desired anti-vibration performance cannot be achieved.
Further, due to the deterioration in elasticity as a result of change with time, the height of these vibration proof rubber members increases (i.e., they extend further downwards), so that the position of the turntable mounted to the second chassis is also lowered. Due to the construction in which the distance between the first chassis and the second chassis cannot be adjusted, nothing can be done about this change with time.
Further, the above change with time does not always occur in the same manner in the four vibration proof rubber members. Variation can sometimes occur between the four vibration proof rubber members, with the result that there is variation in the heights of the vibration proof rubber members. As a result, the parallelism of the turntable cannot be maintained, so that the disk is tilted.
Further, when mounting the second chassis to the first chassis, the screw portions of the cylindrical mounting bolts are passed through the circular mounting holes provided in the first chassis, and the hexagon nuts are threadedly engaged therewith. In this mounting operation, the screw portions of the cylindrical bolts are passed through the circular mounting holes, with the result that a slight clearance is generated between the diameter of the mounting holes and the diameter of the screw portions. Due to this clearance, there is generated a slight positional deviation of the second chassis in the X and Y-directions with respect to the first chassis, so that the position of the turntable mounted to the second chassis is not accurately determined with respect to the first chassis.
Further, in view of the spring constant, a relatively soft rubber material is selected as the material of the vibration proof rubber members, so that these vibration proof rubber members are subject to deformation. The weight of the rotation drive motor, the carriage carrying the reproduction head, etc. arranged on the second chassis, which is suspended from the first chassis through the intermediation of the vibration proof rubber members, is not uniformly loaded on the four vibration proof rubber members, and due to this difference in load, variation in the deformation of the vibration proof rubber members is generated.
Due to this variation in the deformation of the vibration proof rubber members, variation in height dimension, i.e., the distance between the first chassis and the second chassis, is generated between the positions where the vibration proof rubber members are arranged. As a result, it sometimes happens that the horizontality of the upper surface of the turntable, mounted to the second chassis, with respect to the upper surface (upper wall) of the first chassis cannot be maintained, with the result that the disk placed on the turntable cannot be horizontally rotated.